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Although numbers of animals in a given region may fluctuate from year to year, the fluctuations are often temporary and, over long periods, trivial. Scientists have advanced three theories of population control to account for this relative constancy.

The first theory attributes a relatively constant population to periodic climatic catastrophes that decimate populations with such frequency as to prevent them from exceeding some particular limit. In the case of small organisms with short life cycles, climatic changes need not be catastrophic: normal seasonal changes in photoperiod (daily amount of sunlight), for example, can govern population growth. This theory—the density-independent view—asserts that climatic factors exert the same regulatory effect on population regardless of the number of individuals in a region.

A second theory argues that population growth is primarily density-dependent—that is, the rate of growth of a population in a region decreases as the number of animals increases. The mechanisms that manage regulation may vary. For example, as numbers increase, the food supply would probably diminish, which would increase mortality. In addition, as Lotka and Volterra have shown, predators can find prey more easily in high-density populations. Other regulators include physiological control mechanisms: for example, Christian and Davis have demonstrated how the crowding that results from a rise in numbers may bring about hormonal changes in the pituitary and adrenal glands that in turn may regulate population by lowering sexual activity and inhibiting sexual maturation. There is evidence that these effects may persist for three generations in the absence of the original provocation. One challenge for density-dependent theorists is to develop models that would allow the precise prediction of the effects of crowding.

A third theory, proposed by Wynne-Edwards and termed “epideictic,” argues that organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint. However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies.

1. The primary purpose of the passage is to

(A) argue against those scientists who maintain that animal populations tend to fluctuate(B) compare and contrast the density-dependent and epideictic theories of population control(C) provide example of some of the ways in which animals exercise reproductive restraint to control their own numbers(D) suggests that theories of population control that concentrate on the social behavior of animals are more open to debate than are theories that do not(E) summarize a number of scientific theories that attempt to explain why animal populations do not exceed certain limits

2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to

(A) use their theory to explain the population growth of organisms with short life cycles(B) reproduce the results of the study of Christian and Davis(C) explain adequately why the numbers of a population can increase as the population’s rate of growth decreases(D) make sufficiently accurate predictions about the effects of crowding(E) demonstrate how predator populations are themselves regulated

3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease.(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase.(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase.(E) After the number of eagles in Montana decreases, the food supply of this population of eagles also begins to decrease.

6. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?

(A) Thus Wynne-Edwards’ theory raises serious questions about the constancy of animal population in a region.(B) Because Wynne-Edwards’ theory is able to explain more kinds of animal behavior than is the densitydependent theory, epideictic explanations of population regulation are now widely accepted.(C) The results of one study, for instance, have suggested that group vocalizing is more often used to defend territory than to provide information about population density.(D) Some of these studies have, in fact, worked out a systematic and complex code of social behavior that can regulate population size.(E) One study, for example, has demonstrated that birds are more likely to use winter-roosting aggregations than group vocalizing in order to provide information on population size.

Re: Although numbers of animals in a given region may fluctuate from year [#permalink]

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28 Sep 2013, 01:23

We need information from paragraph 2 to answer question 3. Relevant information from the text:1) the rate of growth of a population in a region decreases as the number of animals increases.2) as numbers increase, the food supply would probably diminish, which would increase mortality.3) predators can find prey more easily in high-density populations.4) a rise in numbers may bring about hormonal changes in the pituitary and adrenal glands that in turn may regulate population by lowering sexual activity and inhibiting sexual maturation.

Now the answer choices:

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase.This matches information (1).(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease. This contradicts information (1)(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase. Same problem as choice (B)(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase. This contradicts information (3).(E) After the number of eagles in Montana decreases, the food supply of this population of eagles also begins to decrease. This contradicts information (2)._________________

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Wynne-Edwards's theory says that animals use social displays to convey information about population size. The paragraph ends by saying that this view has been challenged. 6C provides an example of such a challenge: a study that suggests a different purpose for group vocalization, one of the social displays that Wynne-Edwards addresses. E might look tempting, but it merely compares the frequency of two such displays. It still supports the idea that these displays are used for conveying information about population. The other choices all seems to support or build on the theory rather than refute it.
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Re: Although numbers of animals in a given region may fluctuate from year [#permalink]

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11 Feb 2017, 08:31

2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to

(A) use their theory to explain the population growth of organisms with short life cycles(B) reproduce the results of the study of Christian and Davis(C) explain adequately why the numbers of a population can increase as the population’s rate of growthdecreases(D) make sufficiently accurate predictions about the effects of crowding(E) demonstrate how predator populations are themselves regulated

can somebody please explain how the answer to the second question is D?

Re: Although numbers of animals in a given region may fluctuate from year [#permalink]

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13 Feb 2017, 21:19

DmitryFarber wrote:

Wynne-Edwards's theory says that animals use social displays to convey information about population size. The paragraph ends by saying that this view has been challenged. 6C provides an example of such a challenge: a study that suggests a different purpose for group vocalization, one of the social displays that Wynne-Edwards addresses. E might look tempting, but it merely compares the frequency of two such displays. It still supports the idea that these displays are used for conveying information about population. The other choices all seems to support or build on the theory rather than refute it.

Hi Dmitry,

Can u plz explain why we have to search for refuting Whynne's theory option, when it is asking about continuation of the passage ??why is D wrong here ??
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Re: Although numbers of animals in a given region may fluctuate from year [#permalink]

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21 Feb 2017, 01:00

TirthankarP wrote:

Can anyone explain why A is the correct answer in question #3 ?

Because the second theory says that if number increases, then rate decreases. Now come to options.(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase. Contender for correct option. Bcoz if no. decreases, the rate will increase.(B) As the number of woodpeckers in Vermont decreases, the growth rate of this population of woodpeckers also begins to decrease. No. decrease , rate decreases.(C) As the number of prairie dogs in Oklahoma increases, the growth rate of this population of prairie dogs also begins to increase. No increaes, rate increases.(D) After the number of beavers in Tennessee decreases, the number of predators of these beavers begins to increase. No. decreases, predators increases so rate also decreases.(E) After the number of eagles in Montana decreases, the food supply of this population of eagles alsobegins to decrease. No decreases, food decreases, so rate also decreases.

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idivya, we want to refute Wynne-Edwards' theory because that's what's happening at the very end of the passage. These "continuation" questions want us to be very direct. What could we immediately attach to the end of the passage? The last sentence says that some studies have challenged W-E's theory. C follows directly upon that by providing an example of a study that contradicts his theory.

D is the exact opposite of what we want. It says that some studies have supported or extended his work. This would be like saying. "The president claims that violent crime has increased, but some studies disagree. For instance, one study showed that homicides in metropolitan areas had doubled." This directly contradicts what we'd expect, namely, a study showing that violence had gone down!
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Re: Although numbers of animals in a given region may fluctuate from year [#permalink]

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14 Aug 2017, 07:39

All correct in 9 mins 10 seconds, including 3 mins to read .

1. The primary purpose of the passage is to(E) summarize a number of scientific theories that attempt to explain why animal populations do not exceed certain limits ="Although numbers of animals in a given region may fluctuate from year to year, the fluctuations are often temporary and, over long periods, trivial. Scientists have advanced three theories of population control to account for this relative constancy."

2. It can be inferred from the passage that proponents of the density-dependent theory of population control have not yet been able to(D) make sufficiently accurate predictions about the effects of crowding - "One challenge for density-dependent theorists is to develop models that would allow the precise prediction of the effects of crowding."

3. Which of the following, if true, would best support the density-dependent theory of population control as it is described in the passage?

(A) As the number of foxes in Minnesota decrease, the growth rate of this population of foxes begins of increase. -"the rate of growth of a population in a region decreases as the number of animals increases"

4. According to the Wynne-Edwards theory as it is described in the passage, epideictic behavior displays serve the function of(D) regulating sexual activity -A third theory, proposed by Wynne-Edwards and termed “epideictic,” argues that organisms have evolved a “code” in the form of social or epideictic behavior displays, such as winter-roosting aggregations or group vocalizing; such codes provide organisms with information on population size in a region so that they can, if necessary, exercise reproductive restraint. "

5. The challenge posed to the Wynne-Edwards-theory by several studies is regarded by the author with(B) qualified acceptance -"However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies."

6. Which of the following statements would provide the most of logical continuation of the final paragraph of the passage?(C) The results of one study, for instance, have suggested that group vocalizing is more often used to defend territory than to provide information about population density.-"However, Wynne-Edwards’ theory, linking animal social behavior and population control, has been challenged, with some justification, by several studies."The last sentence of last paragraph states that WE theory has been challenged by several studies . C goes ahead by giving an example .
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Re: Although numbers of animals in a given region may fluctuate from year
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14 Aug 2017, 07:39

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